This invention relates to electromagnetically controlled apparatus, such as actuator for accessing a disk file, and relates more particularly to such an apparatus in which damping means are provided for attenuating longitudinal resonances excited in the actuator as it is moved longitudinally by and upon energization of coil of a voice coil motor.
To access disk files, transducers are mounted in aligned spaced relation on a series of parallel arms that are cantilever connected at their respective one ends to a plate secured to a carriage. The carriage/arm assembly is movable longitudinally in response to energization of a coil in a voice coil motor. When the coil was connected directly to the carriage, it was found that there was very little damping in the system, with the result that longitudinal resonances and vibrations exceeded the permissible amplitude limits of the particular servo system used with it. This was especially true in an actuator configuration such as shown herein, which has a minimum of bolted connections which contribute to damping out resonances.
Attempts were made to attenuate this longitudinal resonance by applying many different damping materials to the coil and carriage as constrained and unconstrained damping layers. However, none of these attempts were successful. Since the carriage was significantly stiffer than any of the damping materials applied to the surface of the carriage, it was found that even materials having very high damping characteristics did not significantly improve the effective damping of the longitudinal resonance.
The most pertinent prior art known to applicant will now be described. In the IBM Technical Disclosure Bulletin Vol. 16, No. 6, November 1973, at page 1816, there is disclosed a voice coil/bobbin assembly having a layer of damping material disposed radially between the coil and a reduced diameter portion of an adaptor of a voice coil motor. This damping layer is effective to damp hoop modes of vibration. However, since the end of the coil abuts a shoulder on the adaptor, longitudinal force is not transmitted in shear through the damping layer; and hence, it is not effective to damp longitudinal vibrations or resonances in the coil/adaptor assembly resulting from energization of the coil. Moreover, the damping layer would be subject to extreme temperature change and deterioration since it is in direct contact with the coil.
U.S. Pat. No. 3,194,992 shows a vibration generator in which a cylindrical coil-supporting core overlies and is epoxied to a reduced diameter portion of a table member that is movable longitudinally upon energization of the coil. All of the driving forces between the coil and table member are transmitted in shear; however, since the coil-supporting core is rigidly attached to the table member, and the coil is epoxied to the core, the connection is rigid and there is no damping of the longitudinal resonance in the coil-table member assembly resultant from energization of the coil. The connection is rendered even more rigid by use of a reinforcing band about the overlying portion of the core, and repeated reference to need for an epoxy or adhesive having high shear strength.
In "Machine Design" by Paul H. Black, published 1955 by McGraw-Hill Book Company, Inc., there is shown in FIG. 24-12 (at p. 374) two concentric tubes separated by a rubber damping layer. However, this reference does not suggest incorporation of damping material between two concentric sections of a longitudinally movable actuator. Moreover, the reference implies that one of the tubes is mounted rigidly to a fixed support.
The prior art of which applicant is aware thus does not suggest use of an auxiliary stiffening means disposed in parallel with an elastomeric material that serves as a damping means and primary stiffening means for transmitting shear forces.